1. Field of the Invention
The present invention relates to a honeycomb structure, and more particularly, it relates to a honeycomb structure which is a catalyst support and also functions as a heater when a voltage is applied thereto and which has an excellent heat shock resistance.
2. Description of Related Art
Heretofore, a honeycomb structure made of cordierite, onto which a catalyst is loaded, has been used in treatment of harmful substances in an exhaust gas discharged from a car engine. Moreover, it is also known that a honeycomb structure formed by a sintered silicon carbide body has been used in purification of the exhaust gas (see, e.g., Patent Document 1).
When the exhaust gas is treated by the catalyst loaded onto the honeycomb structure, a temperature of the catalyst needs to be raised to a predetermined temperature. However, the catalyst temperature is low at the start of the engine, which has caused the problem that the exhaust gas is not sufficiently purified.
To solve the problem, a method has been investigated in which a heater made of a metal is disposed on an upstream side of a honeycomb structure onto which a catalyst is loaded, to raise a temperature of an exhaust gas (see, e.g., Patent Document 2).
Moreover, it has been disclosed that a honeycomb structure made of a conductive ceramic material and including both end portions provided with electrodes is used as a catalyst support with a heater (see, e.g., Patent Document 3).